Small particle zeolite containing catalytic cracking catalyst

ABSTRACT

A catalyst composition containing 5 to 50 weight percent of small particle type Y faujasite zeolite is described. A cracking process using the above catalyst can be used to obtain increased conversion of the heavier portion of commercial crudes as well as to generate increased yield of gasoline and distillate.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to the preparation of Y type faujasitezeolite having a smaller than conventional particle size which isformulated into a catalytic cracking catalyst composition that exchibitsa markedly improved liquid product selectivity in the conversion ofheavier boiling modern crude feedstocks.

Thus, the present invention is particularly directed to overcoming theproblem of the increasing utilization of residual oil found in today'scrude oil feedstocks by providing a catalytic cracking catalystcomposition which exhibits exceptionally improved selectivity forconversion of the heavier boiling fraction of hydrocarbon feedstocks aswell as improved selectivity for liquid products, i.e. gasoline anddistillates.

This and other objectives of the subject invention will become moreclearly understood as the description of the invention proceeds.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the preparation and use of crackingcatalyst which comprises small particle crystalline alumino-silicatezeolites dispersed in an inorganic oxide matrix. Particle size ofzeolites is determined conventionally using Scanning ElectronMicrographs (SEM). Presence of agglomeration and intergrowths in Yfaujasite make this estimate uncertain. We have developed a novel methodof measuring an effective (average) particle size by measuring theexternal surface area per unit mass of the zeolite. This measurement isbased on t plot isotherm method described by Lippens and deBoer (Journalof Catalysis, Volume 4, pages 319-323 (1965)) and improvements suggestedby Lecloux and Pirard (Journal of Colloid and Interface Science, Volume70, No. 2, pages 265 to 281 (1979)). T plot is a graphicalrepresentation of volume of nitrogen adsorbed at liquid nitrogentemperature as a function of statistical thickness of N₂ film on a solidsurface. Slope of the t plot is related to accessible surface area. Inan appropriate region of the t plot when adsorption takes placeexclusively on the external surface, slope of the t plot is related toexternal surface area. Effective particle size is defined as thatuniform dimension of cubic particles which yields the same externalsurface area per unit mass as the measured value for a zeolite sample.More specifically, this invention relates to the preparation ofcatalysts which contain small particle synthetic Type Y faujasitematerials having a silica to alumina ratio above 4.5 and an effectiveparticle size range of about 0.05 to 0.3 micrometer.

The preparation of conventionally sized faujasite materials, i.e.materials having effective particle size of 0.3 to 0.4 micrometer isdisclosed in the prior art in U.S. Pat. No. 3,130,007 which describesthe synthetic faujasite designated as "zeolite Y" and other patents suchas U.S. Pat. Nos. 3,185,544, 3,433,589 and 3,574,538 which teach otherversions of essentially similarly sized Y type faujasitic syntheticmaterials.

We will now describe some prior art patents where particle sizedetermined by SEM was used in text and claims.

Canadian 817,405 and 852,713 disclose the use of catalytically activezeolites having a preferred particle size of 200 to 2000 A° (0.02 to 0.2micrometer) and 200 to 10,000 A° (0.02 to 1.0 micrometer) respectivelyto convert heavy hydrocarbons into products of lower molecular weight.The use of catalysts which include a matrix compound is not disclosed.

British 1,223,592 discloses the preparation of Type X crystallinealuminosilicate zeolite which have a predetermined particle size in therange of 0.01 to 100 micrometers. The reference indicates that the verysmall zeolite particles may be combined with a matrix to obtaincatalysts having improved diffusion mol catalytic properties.

U.S. Pat. No. 3,185,544 describes the preparation of crystallinealuminosilicate zeolites from clay which have distinct particles of adefinite size within the range of 0.1 to 5 micrometer. The use ofzeolites having a controlled particle size to prepare petroleum crackingcatalysts is disclosed.

U.S. Pat. No. 3,313,594 describes the preparation of crystallinealuminosilicate zeolite particles of uniform size wherein a significantfraction of the zeolite product may be below 2 micrometers. The uniformsized zeolite product may be used in the preparation of hydrocarbonconversion (FCC) catalysts.

U.S. Pat. No. 3,516,786 describes the preparation of microcrystallinefaujasite-type zeolites having a particle size of 10 to 100 millimicrons(0.01 to 0.1 micrometer) which may be used in the preparation ofcatalytic cracking catalysts.

U.S. Pat. No. 3,755,538 describes a method for preparing zeoliteswherein the particle size may be optimized in the range of 0.1 to 0.3micrometer. The zeolite products are described as having valuablecatalytic properties when used in the preparation of cracking catalysts.

The need to research faujasite material synthesis modifying methodologyparameters to effect product property variations has become particularlyacute in recent times when due to economical and politicalconsiderations it is becoming increasingly important to developpetroleum cracking catalysts which can cope with the high residual oilcontent in today's crude feedstocks.

Until recently, residual oil represented a small (about 10%) portion ofthe crude oil. Relatively inexpensive, light, low sulfur feedstocks wereavailable for cracking. Naphtha, kerosene, and light fuel oil obtainedby simple distillation are usually processed to improve product qualitywithout molecular weight reduction. In a typical refinery, the heavy gasoil (boiling range of about 340°-565° C.) is obtained as a product fromvacuum distillation. The FCC unit reduces the molecular weight of thisfraction primarily to gasoline. The vacuum residual oil is processed tomake coke plus coker gas oil or a residual fuel oil. Recently thisalternative has become less attractive because the high sulfur contentof the residual oil remains in the products and can create SO_(x)emissions during burning of the coke or oil. Furthermore, economic andpolitical pressures have forced refiners to process some of the heavierfeedstocks such as Arab Medium and Arab Heavy. These crude oils containmore vacuum residual fraction and less light products. The residual oilcontains increased amounts of sulfur and contaminant metals. As theamount of residual oil in feedstocks has increased, quality hasdecreased and the market for conventional products such as coke or heavyfuel oil has declined. As a result, some refiners have developedprocesses to convert the vacuum resid to gasoline and other valuableproducts

A recent survey of resid cracking in the United States (P. G. Thiel,Davison 1982 Survey of Residuum Fluid Catalytic Cracking in the UnitedStates, Davison Catalagram, No. 66, 1983, Davison Chemical Division, W.R. Grace & Co., Baltimore, 1983) has shown that between February 1981and October 1982 the number of resid cracking operations has doubled.Most of the refiners are now adding atmospheric bottoms along with theirconventional gas oil feedstocks.

The addition of vacuum bottoms (boiling point greater than 500° C.) tothe feed suggests that some very large asphaltene molecules may bepresent as a liquid aerosol, at least during the initial stages of thereaction. While diffusion limitations do not occur in conventional gasoil FCC units, in resid operations it becomes necessary to crack theselarge nonvolatile components under conditions where diffusionlimitations may play a role in the overall reaction rate.

Among the new challenges faced by the catalyst manufacturer introducedby resid cracking therefore included is the necessity for catalysts todemonstrate improved activity for very large molecules while maintainingat least at previous levels such properties as resistance to metalpoisoning, hydrothermal stability, low coke production and low cost.

After an extensive research program a catalytic product has beendeveloped which has met the afore-mentioned criteria and has thus becomethe object of this invention.

This object has been accomplished by the development of a catalyticcracking process which utilizes a catalyst that comprises an inorganicoxide matrix and a crystalline aluminosilicate faujasitic Type Y zeolitewhich is characterized by smaller than conventional particle size. Asstated previously, commercial Type Y zeolite is typically characterizedby an effective particle size of about 0.3 to 0.4 micrometer, while theeffective particle size characterizing the Type Y zeolite used in thecatalysts and process of the present invention lies in the 0.05 to 0.3micrometer range.

The invention's objectives were accomplished on the basis of thefollowing rationale.

In order to be effectively converted to more valuable products, oilmolecules must reach the external surface of the catalyst particle anddiffuse through the pore structure to an active site. The reactants mustthen adsorb and react on the site. The products must then desorb,diffuse to the outer surface, and desorb from the particle into the bulkgas stream.

Residual oil is typically composed of very large molecules, a fractionof which boil above about 500° C. [J. G. Speight, Chemistry andTechnology of Petroleum, Dekker, New York, 1980 and R. L. Richardson 2ndS. K. Alley, Div. Pet Chem., Prepr., Am. Chem. Soc., 20(2), 554 (1975)].Some may even be present in the form of an aerosol liquid duringintroduction and reaction in an FCC unit. This presents two problems.Both liquid and gas molecules must diffuse through the matrix to thezeolite, and then must react. Molecules of 20 A° or greater in diametercannot be cracked easily inside the zeolite pore structure which is onlyaccessible through 8-9 A° openings. Instead they are restricted toreaction on the external surface of the zeolite particles or to cagesvery close to the external surface. As a result, there are observablediffusion restrictions within the zeolite and a loss of activity foreven moderate size molecules.

The catalyst product of the subject invention by exhibiting excellentconversion characteristics for these low boiling heavy hydrocarbons andby demonstrating superior selectivity for producing liquid products suchas gasoline plus distillate obviously overcomes the problems encounteredby conventional Type Y zeolite catalysts by virtue of its reducedparticle size. The small particle faujasite has an increased externalsurface area (e.g. 50.9 m² /g equivalent to an effective particle sizeof 0.06 micrometer as compared to 9 m² /g equivalent to an effectiveparticle size of 0.33 micrometer for conventional type Y faujasite) andactivity as well as selectivity studies conducted have indeed shown thatwith a heavy resid feed the small particle sieve catalyst of the subjectinvention is both more active and yields more liquid product.

This increased surface area resulting from the decreased particle sizeprovides the necessary external surface site for the residual oil'slarge molecules to crack, offsetting thereby the effect of diffusionrestrictions within the zeolite.

Having thus elaborated on the background and on the essence of thesubject invention we now proceed with a description of the moretechnical aspects thereof.

Basically, what has been done was to first produce the small particleType Y zeolite, i.e. faujasite of a 0.05 to 0.06 micrometer effectiveparticle size, according to the known procedure taught in U.S. Pat. No.3,755,538. Secondly, the same procedure was used to produce a scaled upbatch of said small particle Type Y zeolite in order to, thirdly,incorporate it into a cracking catalyst prepared according to the knownproceoure taught in U.S. Pat. No. 3,957,689, said cracking catalystbeing a composite of the small particle rare-earth exchanged Type Yzeolite clay, and a silica-alumina sol. Finally, in order to runcomparative examples a cracking catalyst was prepared according to thesame procedure taught in U.S. Pat. No. 3,957,689 which resulted in theabove described product with the only difference being that conventionalcommercially available rare earth exchanged Type Y zeolite, i.e. Type Yzeolite of effective particle size 0.33 micrometer, was used.

Tests for comparative purposes were run on both of these catalysts byusing a heavy oil cracking feed (73% boiling above 482° C.) and theresults clearly demonstrated the superior performance of the invention'ssmall particle Type Y zeolite catalyst composition over that of aconventionally sized Type Y zeol ite containing catalyst composition aswill now be shown in the following specific examples.

EXAMPLE 1

Preparation of small particle sodium Type Y zeolite (NaY) faujasite(according to the teachings of U.S. Pat. No. 3,755,538).

A solution of dilute sulfuric acid containing 68 g concentrated sulfuricacid (96% H₂ SO₄) is mixed with 200 ml water into a solution of 1,096 gsodium silicate solution (41° Be: ratio 1.0 Na₂ O:3.22 SiO₂) dilutedwith 400 ml water. A solution comprising 149 g sodium aluminate (21.4%Al₂ O₃ ; 18.2% Na₂ O) diluted with 170 g water is added. Finally 605 gseeds, whose oxide ratio is 16 Na₂ O:1.0 Al₂ O₃ :15 SiO₂ :320 H₂ O, thepreparation of which is taught by U.S. Pat. No. 3,574,538, is added tothe blend. The resulting mixture of all of the above chemicals has theeffective slurry oxide ratio of 6.5 Na₂ O:1.0 Al₂ O₃ :16 SiO₂ :280 H₂ Oand was poured in a two liter polypropylene bottle, which was looselycapped. The bottle was then placed into an oven heated at 100±1° C.After the bottle was heated for 12 hours in the oven the slurry wasfiltered on a Buchner filter and the filter cake was rinsed three timeswith hot water. The filter cake was dried at 105±5° C. and a portion wasanalyzed by powder X-ray diffraction. The product was found to be ahighly crystalline sodium Type Y zeolite having a unit cell size of24.66 A and a SiO₂ /Al₂ O₃ ratio by chemical analysis of 5.0. Effectiveparticle size of this sample by t-plot method was measured as 0.06micrometer.

EXAMPLE 2

Preparation of Large Batch of Small Particle NaY

The process of Example 1 was essentially scaled up to yieldapproximately 5 kg of dry small particle faujasite. Two solutions andone slurry were prepared. Solution A was dilute sodium aluminatesolution made by mixing 4,305 g sodium aluminate solution (21.4% Al₂ O₃:18.2% Na₂ O) into 6,400 g water. Solution B was made by mixing 1,981 gconcentrated sulfuric acid (96% H₂ SO₄) with 9,800 g water. A slurry wasmade from a mixture of 31.0 kg commercial sodium silicate (41° Be; 1.0Na₂ O:3.22 SiO₂ ratio) with 6.8 kg water and 17.54 kg seeds. Each of thethree chemicals--Solution A, Solution B, and the slurry composed ofsilicate, seeds, and water--was fed to a high speed mixer by its ownpump. Solutions A and B were pumped at about 500 ml/min. while theslurry was pumped at about 2.8 liters/min. The slurry formed by themixing of the three components was transferred to a 20 gallon closedreactor heated by a steam jacket and fitted with a condenser. After theslurry was placed into the reactor, it was heated with rapid stirring to100±1° C. Then the mixer was turned off and the heating was continuedfor 9 hours. The crystallized slurry was filtered on a 50 cm Buchnerfilter and the filter cake washed with four 10 liter portions of hotwater. A portion of the filter cake was dried at 105° C. and analyzed bypowder X-ray diffraction. The product was found to be highly crystallineNaY faujasite zeolite which had a unit cell size of 24.66 A, a SiO₂ /Al₂O₃ ratio of 5.0 by chemical analysis and a nitrogen surface area of 941m² /g as measured by the BET method by a Digisorb 2500 instrument madeby Micromeritics, Inc. of Norcross, Georgia. T plot effective particlesize was measured as 0.06 micrometer. Portions of the batch of smallparticle NaY were made into various types of petroleum crackingcatalysts and compared with commercial NaY zeolite as illustrated by thefollowing examples.

EXAMPLE 3

Cracking Catalyst Made from Small Particle NaY, Clay and Silica-AluminaSol

A petroleum cracking catalyst was made as follows according to theteachings of U.S. Pat. No. 3,957,689. A silica alumina sol was made byrapidly mixing a stream of sodium silicate solution, Solution A (12.5%SiO₂ made from the commercial sodium silicate as used in Examples 1 and2 above), against a stream of acidified aluminum sulfate solution,Solution B (12.2% sulfuric acid and 30 grams/liter of aluminum sulfateAl₂ (SO₄)₃.16 H₂ O).

Solution A and Solution B were rapidly mixed together in a high speedmixer in the approximate ratio of 1.5 l Solution A to 0.5 l Solution Band holding the pH at 3.1±0.1 until 12.0 kg sol was formed. Then 4,247 gkaolin clay (RC-32 kaolin from Thiele Kaolin Co. or Natka kaolin fromNational Kaolin Co. are suitable) were blended into the sol. Next aslurry of 986 g of particulate alumina (Al₂ O₃.H₂ O) having a totalvolatiles content or loss upon ignition of 25.4%, was slurried in oneliter of water and acidified to pH 4 and added to the sol-clay-mixture.Lastly a slurry of 2609 g of filter cake of the small particle NaY(total volatiles=77%; Na₂ O=13.2%) acidified to pH 4 was added to thesol-clay-alumina mixture. Then the slurry was spray dried in a Bowenspray dryer using an inlet temperature of 316° C. and an outlettemperature of 149° C.

A 3,000 g portion of the spray dried product was slurried in 11.3 l hotdeionized water at 60°-71° C. and filtered. The filter cake was rinsedthree times with 3 l of hot water. Then the cake was reslurried in 9 lof hot water and filtered again. The cake was rinsed three times with 3l portions of hot water. The filter cake was next reslurried in 10 l ofhot water and 215 ml of mixed rare earth chloride solution (60 wt.%RECl₃.6 H₂ O) were mixed into the slurry. The slurry was gently stirredfor 20 minutes and kept at a temperature of 60°-71° C., and the pH waskept at 4.7-5.2. Lastly the slurry was filtered again and rinseo withthree 3 l portions of hot water. The product was dried and found to be amicrospheroidal, fluid catalyst which had a particle size in the range40-120 micrometers.

EXAMPLE 4

Cracking Catalysts Made from Commercial NaY, Clay and Silica Alumina Sol

A similar catalyst similar to text of Example 3 was prepared using acommercial conventional NaY zeolite that has a SiO₂ /Al₂ O₃ ratio ofabout 4.9±0.1 and a t plot effective particle size of 0.33 micrometer.The finished catalyst was then oven dried at 149° C.

EXAMPLE 5

The catalysts prepared according to Examples 3 (small particle size) and4 (conventional particle size) were here tested as follow.

Heavy oil cracking feed (HOC) in which about 73% boiled above 482° C.,was cracked in the microactivity test using the test procedure publishedby F. G. Ciapetta and D. S. Henderson entitled "Microactivity Test ForCracking Catalysts". Oil and Gas Journal, Vol. 65, pages 88-93, Oct. 16,1967. Microactivity tests are routinely used in the petroleum industryto evaluate cracking catalysts in the laboratory. The HOC feed wascracked over these catalysts using the following test conditions.

Temperature=515.6° C.

Weight Hourly Space Velocity (WHSV)=16

Catalyst to oil ratio was varied to investigate the yield of liquidproducts at different operating conditions.

HOC feed was passed through 5.0 g of catalyst. The products werecollected and the percent conversion of gas oil into hydrogen, lightgases, gasoline range hydrocarbons, etc. was determined by gaschromatography. Conversion of the heavier boiling fraction of the feed(fraction boiling above 482° C.) was also determinedchromatographically.

The results of these compartive heavy oil cracking tests were tabulatedas shown below and they provide the concrete evidence necessary to provethe superiority of the invention's small sized 0.06 micrometer Y-typefaujasite comprising catalyst over the conventional 0.33 micrometersized Y-type faujasite comprising catalyst both in terms of improvedselectivity for liquid product and in terms of improved conversion ofheavier boiling fraction of cracking feed.

    ______________________________________                                                          Example 3                                                                             Example 4                                                             Product Product                                             ______________________________________                                        Effective Particle Size of                                                                        .06       .33                                             Y type faujasite, micrometer                                                  Catalyst Formulation (Wt. %)                                                  Zeolite             10        10                                              SiO.sub.2           20        20                                              Al.sub.2 O.sub.3 from SRA                                                                         10        10                                              Clay                60        60                                              Chemical Analyses                                                             Na.sub.2 O          .24       .36                                             RE.sub.2 O.sub.3    2.48      2.12                                            Reactor Test Data                                                             After Indicated Deactivation-S13.5.sup.(1)                                    1.  Catalyst to oil ratio:                                                                            2.9    3.8   2.9  4.0                                 2.  Standard Conversion, V %:                                                                        74.4   76.9  73.3 80.4                                 3.  C5.sup.+  Gasoline, V %:                                                                         60.6   64.9  61.3 61.5                                 4.  Distillate, V %:   16.9   15.7  15.7 13.6                                 5.  G + D, V %:        77.6   80.6  76.9 75.0                                 6.  Average G + D, V %: 79.1      76.0                                        7.  Conversion of heavier                                                                            98.2   98.5  95.9 98.2                                     boiling (above 482° C.)                                                fraction of the feed:                                                     8.  Average conversion of                                                                             98.4      97.1                                            the heavier fraction                                                          of the feed:                                                              ______________________________________                                         .sup.(1) Steam deactivation: 8 hours @ 732° C., 100% steam, 1.1        kg/cm.sup.2 pressure of steam.                                           

As may be concluded from the preceding tabulation of comparative resultsof catalytic cracking tests conducted using the invention's small sizeType Y zeolite promoted catalytic composition versus a catalyticcomposition containing conventionally sized Type Y zeolite, the former'saverage conversion of the heavier fraction of feed and the former'saverage increase in production of gasoline and distillates exceed thoseof the latter.

Obviously, many modifications and variations of the invention may bemade without departing from the essence and scope thereof and only suchlimitations should be applied as are indicated in the appended claims.

What is claimed is:
 1. In a petroleum catalytic cracking process, amethod of increasing the conversion of a heavy hydrocarbon fraction of afeedstock and of producing higher yields of liquid products, said methodconsisting in the use of a Y zeolite containing catalytic crackingcatalyst wherein said Y zeolite is dispersed in an inorganic oxidematrix the improvement comprising the use of a Y zeolite characterizedby a t plot external surface area of up to 100 m² /g and an effectiveparticle size in the range of 0.03 to 0.3 micrometer.
 2. The methodaccording to claim 1 further characterized in that the Y zeolite has asilica to alumina ratio above 4.5.
 3. The method according to claim 1wherein greater than about 20 weight % of said feedstock boils aboveabout 482° C.
 4. A catalytic cracking catalyst composition forcontacting heavy hydrocarbon feedstocks that contain at least 20% byweight hydrocarbons that boil above about 482° C., comprising aninorganic oxide matrix, and a Y zeolite having a t plot external surfacearea of up to 100 m² /g and an effective particle size 0.03 to 0.3micrometer.
 5. The composition of claim 4 wherein said catalyst containsfrom about 5 to 50 by weight of said zeolite.
 6. The composition ofclaim 4 wherein said inorganic oxide matrix comprises silica, alumina,silica-alumina gels, cogels and sols, clay and mixtures thereof.
 7. Thecomposition of claim 4 wherein said Y zeolite is selected from the groupcomprising ultrastable Y, rare earth exchanged Y and mixtures thereof.